Method of treating furnace carbon black



United States Patent- 6) 2,707,672 METHGD' F "IREATINGFURNACE- CARBON BLACK Carl W. sweitzerg-Garden'city; N, Y., assignor-to Columbian Carbon Company No Drawing. Application March 9, 1949, SeriaLNo. 80,572

2. Claims.. (Cl. 23--209.1)

The present invention relates to carbon blacks, and more particularly to carbonblacks of the type known as furnace carbons. It provides anovel and very useful-carbon black product having a unique combination of characteristics. It-further provides a novel process'wherebythe product may, with advantage, be. produced;

In my copending applications, Ser. No. 80,571, filed concurrently herewith, now abandoned and SeriaINo. 322,589; filed November 25, 1952,, asa-continuation-inpart of application Serial No. 80,511, I-havedescribed and'cl'aimed a novel process wherebyfurnacc carbons may be fully oxidizedto a pHvalue ofabout-2.5'to-3;5 without perceptible loss in weight by'burning and without change in particle sizeor surface area. My'presentprocess is a modification of the process ofsaidapplications and results in a furnace carbonhaving afully oxidized surface, of intense blackness and. markedly increased oil absorptionand iodineadsorption characteristics.

In accordance with the process .oftmy copending applications just noted, the. furnace carbon is uniformly heated to a temperature in the black-heat range of'theparticular' carbon being treated but to at least 650 F; and'air, orair mixedwith steam, is passed in contactiwith theheated carbon. The. temperature range. to which the black. isheated'may bewellbelow the ignition temperature'of the furnace carbon, but, advantageously, the temperature should'be only sufliciently below the ignition temperature. ofthe carbon to avoidlocalizedaglowing. or bright spots. The temperaturewill vary somewhat with.the particular furnace black.-treatedand'whether or not. steam is mixed with the air. The maximum temperature possible withoutglowing is usually most advantageous as the required treating -time-is thereby minimized.- In' general, Where-- substantial proportions of: steam, e. g., to by volume, are I mixedwith the air, oxidizing temperatures approximately.50'F-. higher: than possible with air alone may, with-advantage; beemployed; The-maximumpermissible-temperature has generally-been foundnottoexr. ceed 1,100. P. and-with most furnace blacks'should'not exceed 1,000 F.

In said,;process, the optimum treating time is largely. dependent 'upon thetreating temperature employed. The oxidation'rate increases with an increase in temperature, with proportionate tdecreasein treating time, as justnoted; The optimum time factortor any particular. furnacecarebon ate-given oxidizing temperature is readily determined by periodically: sampling the. blackbeingoxidizeds and testing the samples for pH characteristics; At maximum oxidation,- the pH -characteristics off'the black will reach a minimum, usuallyabout 235; Insome instances; the minimum attainable pH has been found-to range" as; high as'3l5j thus varying somewhat for different blacks; When the minimum attainable pHfva-lue is reached, the treatment. is immediately discontinued;

The. process. may be carriedout by. heating theblack in shallow bedsnot exceeding A. inch in. thickness to, the desiredblack-heat temperature while passing; air or: a

2 mixture off air. and steam over the black. The treatment may be carried-outin'shallow trays-in a heated oven.

lhave now. discovered that ifthe'treatment in accord ance with the processof said copending application be continued beyond the point ofrcomplete-oxidation of the carbon surfaces, as indicated by the-minimum obtainable pH? characteristics for'the particular carbon, a remark able change in the properties-of the carbon takes place, Inth'e first stage of the treatment during whichthe'carbon. surfaces are completely oxidized," only those changesassociated'with increased oxidation are apparent. For instance, there is a gradual lowering-of'pI-I, an increase in the capacity of the carbon to adsorb alkalis, an in-' crease in volatile content, andan increase in the flow= characteristics in ink, and a retarding'of the curing-ofrubber in which the resultant black is compounded. There are, however, no changes in other fundamental propertiesof the black, such as color, oil absorption, and iodine adsorption. 7

Where this-:treatment is continued, in accordance with' my present process, theother properties of the-carbon developed at thepoint of full surface oxidationv remain constant, but the color becomes'gradually blacker, the oilabsorption characteristics. gradually higher, and theiodineadsorption increases rapidly. A loss in weight is also observed,- but this loss is far less than that experienced in conventional'methods" of oxidizingchannel blacks to efiect a-comparable color change;

Reference herein to color characteristics of the'carbons refer to the color, as indicated'by the'ABC color-scaledetermined by the method described in the article by Sweitzer and Goodrich, appearing'in Rubber Age for- August 1944, pages 469, 478 Color change of a particular carbon black has been foundto be adependable index. to changes in surface area by partial consumption in an oxidation treatment such as herein described whether carriedout at a glowing temperature, in-accordance-withprior art processes, or atblack-heat temperatures, in'a'c cordance with my presentprocess. It hasalso beensup posed that color isa dependableindexto particle size diameters offthecarbon. In general, an increase in the color indextis'indicative of. an.increase. in vsurface a'rea; a tenshade increase inhlacknessbeing roughly equivalent to one acre per pound increase in surface area.

As previously. noted though some, loss in weight is experienced, thisloss is much less. by my process than, that experienced in the oxidationof channel blacks by conventional methods for comparable color increases. I have found, for instance, that ifa high modulusfurnace carbon having a surface area of 5 acres per pound; equivalent to a mean particle size diameter of 60lmilli, microns, be treated in accordancewith my present process until the.weight loss is equal to 50%, the color index of. the carbon will have been increased from to 150, the latterv beingjndicative of atsurface areav of about 10' acres per pound, equivalent to a mean particle size diameter of 30 millimicrons. But, to efiecta 50% reduc. tionin the mean particle size-diameter of a carbon would require the oxidizing away of of the.original'volurne of? the carbon particle. Since by my process only 50% of the original weight'ofthe carbon. is lost, it is readily apparent thatthe increase in color is due, in part at least, to somethingother than decrease in mean. particle size diameter.

Investigation by X -ray analysis substantiated by confirmatory tests such as iodine adsorption, the latter being indicative of total surface areas, indicatesthat, under, the" conditions of my present process, there is a selective oxidizing away of crystallites within the carbon particles resulting. in the surface of the particles-becoming.deeply. etched or. pitted, This etching or pitting has.been;found. to-continue until atleast one-half ofthe carbon particle has been oxidized away by my black-heat, low temperature oxidation. It now appears that the increased blackness of the carbon is due to the absorption of light in these tiny pits or craters on the surface of the carbon particles, as distinguished from drastic reduction in the mean particle size diameter of the carbon by burning away the greater part of the carbon as in the prior methods for treating channel blacks.

A further desirable property of carbon blacks intended for use in printing inks is a blueness of tone. This tone blueness has been ascribed to the coarseness of the particles, the coarser the particles, the bluer the tone. Where carbon blacks have been treated by prior art methods to increase their blackness, there has been a loss of much of this desirable blue tone property due to the drastic reduction in particle size. By my process, the desired blackness may be attained without a commensurate reduction in mean particle size diameters, while retaining to a major extent the blue tone of the original furnace black. The increased oil absorption and iodine adsorption characteristics of my product likewise appear to be due to the greatly increased particle surface occasioned by the pitting of the carbon particles.

The invention will be further described and illustrated by the following specific example of the application of the process to the treatment of a high modulus furnace carbon having an ignition temperature of about 950 F. The black was spread in thin layers in shallow trays in an electrically heated furnace and maintained at a temperature of 900 F. for a period of 150 minutes, while passing air by natural draft over the surface of the carbon beds. During this treatment, 50% by weight of the carbon was lost due to oxidation. The characteristics of the carbon before and after treatment are set forth in the following Table I.

Substantially identical results were obtained by heating the black to a temperature of 950 F. and maintaining this temperature for a period of 120 minutes while passing a mixture of air and steam by natural draft over the carbon, instead of air alone as in the preceding example.

These operating conditions have been found optimum for this particular type of carbon, but may be changed somewhat with comparable results provided the temperature does not exceed the ignition temperature of the particular carbon being treated, but is at least about 650 F. Temperatures lower than those specifically illustrated may be used but a longer treating time will be required. It is usually desirable, as previously noted, to employ temperatures as high as possible without causing local glowing or ignition of the carbon as, at the higher temperatures, comparable results may be obtained in a shorter period of time. Likewise, the invention contemplates discontinuing the treatment at an intermediate point between that where complete surface oxidation is obtained without loss of weight and maximum increase in blackness, oil absorption and iodine adsorption to obtain a product with intermediate properties.

The relationship between time of treatment, percentage weight loss, and development of changes in characteristics is illustrated by the following examples using the same type of carbon black used in the preceding example and operating at 950 F. using a mixture of air and steam. The time in-minutes, the color on the ABC color scale 4 and the percent weight loss are set forth in the following Table II.

Table II Percent Weight Loss Time As indicated by the foregoing Table II, the second stage of the treatment may be varied in intensity depending upon the desired characteristics of the product, for instance, color, oil absorption and iodine adsorption. The intensity of the treatment may be varied either by varying the time, or the temperature, or the composition of the oxidizing gas, that is, where air alone or air plus steam is used. Frequently, carbon dioxide may, with advantage, be used in place of the steam.

The loss in weight has been found to be a dependable indication of the change in ABC color number regardless of the particular treating temperature or whether air alone, or air plus steam, or air plus carbon dioxide is used, as indicated by the test data given in the following Table III representing five runs treating the identical furnace carbon under various conditions. The data in the first column represents the loss in weight based on the original weight of furnace carbon treated and the data in the remaining columns represents the ABC color numbers of the respective samples at the point where the indicated weight loss has occurred. The data in the secr ond and third columns are taken from runs in which a mixture of air and steam was passed by natural draft across the surface of the heated carbon, the carbon of run #1 having been heated uniformly to 950 F. and that of run #2 having been heated at 900 F. In run #3, a mixture of free air and carbon dioxide was passed gently by natural draft across the surface of the carbon uniformly heated to a temperature of 900 F. In runs #4 and #5, the carbon was heated to a temperature of 900 F. and subjected to air alone, the air of run #4 being forced air blown gently against the surface of the carbon bed, while the air of run #5 was blown gently across the surface of the carbon bed. The ignition temperature of the black treated was about 950 F.

Table III ABC Color No. Weight Loss, Percent Run #1 Run #2 Run #3 Run #4 Run #5 Loss in weight and change in ABC color has also been found to be a convenient index to changes in oil absorption and iodine adsorption for a particular furnace black. In general, the second stage of the process should be continued until the loss in weight is at least 5% in order to elfect an increase in color, oil absorption and iodine adsorption of practical significance or commercial value. Also, it is generally undesirable to continue the treatment beyond the point where loss in weight is 50%-60% of the starting material. With some furnace carbons, noticeable changes are effected even at 2% weight loss and practical advantages are usually attained when as little as %10% of the' carbon hasbeen consumed. Additional advantages in color, oil absorption-and"-iodine adsorptionmay be.attained by continuing the treatment until as high as 75 by weight; of'the'carb'onhas been consumed.

The invention will be further illustrated by the:follo,wing;specific.examples of its applicationand theresultant product set forth in Table 1V, in.each,of which the furnace black. treated was a highmodulus furnace black havingan ignition temperature of about 950 F. and other characteristics indicated in the line opposite the notation .Control. Changes in these. characteristicsby treatment. in' accordance with my process to the points where the indicated weight loss were experienced are indicated in the linesfollowing the-indicated weight loss. In each test, the black was heated to-a temperature of 950 F. while blowing air by natural draft over the heated black.

Table IV ABC. OiIabsorp- I Color tion ge1s./ 2 No. 106 lbs. mm X10 Control It will be observed that, where the treatment is extended to weight losses greater than about 50%, values obtained for color and oil absorption are somewhat erratic.

A structure furnace carbon having an ignition temperature about 900 F., a color index of 111 and an oil absorption number of 16.4 was heated to a temperature of 920 to 950 F., while passing a mixture of air and steam across the surface of the black by natural draft. Samples of the black Were taken periodically and tested for color and oil absorption. Loss in weight was also determined at the time of taking each sample. The test results are set forth in the following Table V.

Table V Percent 011 Abhme wt. loss Color sorptlon A further furnace carbon of still higher structure having an ignition temperature of about 1,000 E, a color index of 89 and an oil absorption of 15.6, was heated to 950 to 1,000 F. in the presence of air and steam and samples taken and tested as in the preceding example. The results of this test are set forth in the following Table VI.

treatment resultedin a weight loss of-"42% and amincrease in color and'oilabsorption to- 144 and23 4; re spectively.

Lamp blacks may also be treated-with marked advan tage by my present process. For instance; under the conditions of the preceding example, the color of=a lamp black was increased from 76 to 145. Under identical conditions, the color of a second carbon, a furnaceblackawas increased from 113 to- 152 with a 40% weightloss -and' thecolor of a still further furnace black was increased from 147 to 175 with a 49% weight lossandan'increase in oil absorption from 11.0 to 18.3;

The oil absorption values referred to v hereinare-hp terms of gallons of linseed oil per 100 pounds of the black determined by the stiff paste oil absorption test methoddescribed in detail on page-475' of Rubber Age for August 1944.

Asillustrated by the foregoing specific examples, the characteristics of my new product, with theexception-of pH'value, may be varied over a considerable-range by extending the treating period, or otherwise varying the severity of the treatment.- The pH value is in each instance the minimum attainable for the particular black, since the surface of the black is fully oxidized. Depending upon the severity of the treatment, and somewhat upon the initial characteristics of the black, I may produce carbons having a fully oxidized surface, an ABC color number within the range of to 175, a stiff paste oil absorption value of 11 to 24 gallons per pounds of the black and an iodine adsorption value of 25 to 200 equivalents per gram 10 It will be understood that the terms furnace blacks and furnace carbons, appearing in the appended claims are to be interpreted to include lamp blacks.

In the foregoing examples of specific operations, in accordance with the present invention wherein the oxidizing air was used in admixture with steam, the proportion of steam to air was, in each instance, within the range of 1:3 to 1:10.

The carbon black of my present invention possesses a unique combination of properties by reason of which it is particularly adapted to the manufacture of printing inks, paints, varnishes and the like. It has the tinting strength of fine impingement carbon black in combination with the blue tone of much coarser carbons. It has the flow characteristics of a long ink carbon and the smoothness of a lamp black.

The product resulting from the preferred modification of the present invention is characterized by a unique combination of properties including pH characteristics within the range of 2.5 to 3.5 and ABC color number Within the range of 140-160, stifi paste oil absorption characteristics of 15 to 25 gallons per 100 pounds, the iodine adsorption value of 150 to 200 equivalents per gram 10* and a blue tone. The color, oil absorption and iodine number characteristics are, however, subject to somewhat wider latitude depending upon the initial characteristics of the furnace black treated and the extent of treatment as measured by the Weight loss.

In general, it has been found that there is a 10 point increase in ABC color number for each 10% Weight loss of the furnace black. Thus, when a furnace black initially having an ABC color number of 100 is treated in accordance with the present invention to a 10% weight loss, the ABC color number of the resultant carbon will be 110. There is a substantially straight line relationship extending as far as about 75% weight loss, beyond which the process ceases to be commercially feasible. At a 20% weight loss of this carbon, the color number is at a 30% weight loss, the color number is about at a 40% weight loss, the color number is about at a 50% weight loss, the color number is about 150, and so on.

In general, it may be said that the initial stiff paste oil absorption value of the carbon black may be doubled by the present process. Oil absorption and also iodine adsorption of the finished product will depend not only upon the original characteristics of the furnace black, but also upon the extent of treatment measured by the weight loss, as previously indicated.

I claim:

1. Process for the treatment of furnace blacks which comprises uniformly heating a quiescent, shallow bed of the furnace black, of a thickness not exceeding about inch, to a black-heat temperature not lower than 650 F. but below the ignition temperature of the particular black and not exceeding 1,100 R, no portion of the bed of black being permitted to exceed a black-heat temperature, while passing air over, and in contact with, the surface of the bed of heated black until the surface area of the particles of the black has been completely oxidized as indicated by the minimum attainable pH characteristic, within the range of 2.5 to 3.5, and then continuing the treatment at a black-heat temperature until at least 5% but not exceeding 75% of the black by weight has been consumed without ignition.

2. Process of claim 1 wherein the second stage of treatment is discontinued before in excess of 60% of the black has been consumed.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Swcitzer et al.: The Rubber Age, vol. 55, No. 5, August 1944, pages 469-478.

Braendle et al.: Carbon pH and Structure in Rubber Compounding, India Rubber World, vol. 119, No. 1, New York, October 1948 (pages 57-62). Presented before the A. C. S. April 22, 1948. 

1. PROCESS FOR THE TREATMENT OF FURNACE BLACKS WHICH COMPRISES UNIFORMLY HEATING A QUIESCENT, SHALLOW BED OF THE FURNACE BLACK, OF A THICKNESS NOT EXCEEDING ABOUT 1/4 INCH, TO A BLACK-HEAT TEMPERATURE NOT LOWER THAN 650* F. BUT BELOW THE IGNITION TEMPERATURE OF THE PARTICULAR BLACK AND NOT EXCEEDING 1,100* F., NO PORTION OF THE BED OF BLACK BEING PERMITTED TO EXCEED A BLACK-HEAT TEMPERATURE, WHILE PASSING AIR OVER, AND IN CONTACT WITH, THE SURFACE OF THE BED OF HEATED BLACK UNTIL THE SURFACE AREA OF THE PARTICLE OF THE BLACK HAS BEEN COMPLETELY OXIDIZED AS INDICATED BY THE MINIMUM ATTAINABLE PH CHARACTERISTIC, WITHIN THE RANGE OF 2.5 TO 3.5, AND THEN CONTINUING THE TREATMENT AT A BLACK-HEAT TEMPERATURE UNTIL AT LEAST 5% BUT NOT EXCEEDING 75% OF THE BLACK BY WEIGHT HAS BEEN CONSUMED WITHOUT IGINITION. 